Low-noise, large dynamic-range sensor for measuring current

ABSTRACT

A low-noise current sensor enables large dynamic range current measurements of alternating and direct current flows. The current sensor includes a first substrate, a first conductor, a magnetic flux conductor comprising a first portion orthogonal to the first conductor and a second portion, the second portion penetrating the first substrate, an inductive sensor comprising a first plurality of loops around the second portion of the magnetic flux conductor on the first substrate, wherein the first plurality of loops is orthogonal to the second portion of the magnetic flux conductor, and a Faraday cage that encloses the first plurality of loops and separates the first plurality of loops from the first conductor.

Cross-reference to related applications

This application is a Continuation of U.S. application Ser. No.17/086,125, filed Oct. 30, 2020, and issued as U.S. Pat. No. 11,029,341on Jun. 8, 2021, which claims the benefit of Provisional application No.62/929,657, filed Nov. 1, 2019, the contents of which are incorporatedherein by reference in their entirety.

Background

With the advances in wired and wireless networks enabling the “Internetof Things,” it becomes clear that remote management would benefit fromsensitive and accurate monitoring of current flow.

Advances in AC waveform analytics and embedded microcomputers have ledto real-time in-depth circuit analyses, including electric motormanagement and precise power control. It is possible to use waveformanalytics to estimate instantaneous power draw; and from the measurementof power consumption, real-world activity can be inferred moreaccurately than from other measures. For example, accurately sensing thefirst few cycles of an alternating current motor at start up will yieldsignificantly more information when coupled with accelerometer data thanthe accelerometer data can yield by itself.

Accurate current waveforms and accelerometer data will directly yielddata concerning gear trains, road conditions, inclines, gross vehiclemass and even details about a motor's physical condition and maintenanceneeds. These measurements can be collected and refined as historicalmodels to become another layer of analytical tools which can be used forcontrol, and to infer both maintenance and operational variances fromexpected norms.

Measuring low-frequency electrical current in a conductor is usuallyperformed by exploiting one of two well known relationships associatedwith current flow. The first relationship is known as Ohm's Law and itrelates voltage and current to a known resistance. One type of currentsensor that uses Ohm's law to measure current is called a current shuntor a shunt current sensor. The voltage is measured across a knownresistance: using the measured voltage as the dividend, the knownresistance as the divisor, the value of the current as an RMS (Root MeanSquare) quantity is the quotient. This method is problematic when highcurrents are measured, as even minimal calibrated resistances willconvert power to heat by the current squared multiplied by theresistance (I²R) relationship, which can be significant and represents aloss of efficiency.

The second well known relationship for measuring low-frequency currentis Faraday's Law. Faraday's Law states that a time-varying currentflowing in a conductor causes a perfectly orthogonal flux emission of amagnetic wave which is proportional to the magnitude of current flow.The time-varying flux causes an induced voltage in a closed loop of wirethat is cut by the flux. Capturing a representative measure of the fluxemission can be accomplished using a suitably constructed cut loop (anantenna) terminated in a matching impedance. The complicating issues arearranging the antenna to be perfectly orthogonal and limiting thereceived magnetic emission to be the one intended to be captured.

Another, more recently discovered, relationship associated with currentflow that offers a method of measurement is known as the Hall Effect.The Hall Effect is something of the same phenomena expressed asFaraday's Law, but this time the effect of the current flow-induced fluxis measured within the conductor itself. The flow of current in aconductor causes a magnetic flux orthogonal to the flow of the current.The magnetic flux pushes the negatively charged electrons to one side ofthe conductor. The pressure of this push is directly related to themagnitude of the current flow. The resulting electric potential acrossthe conductor at right angles to the flow of the current is measured asa voltage that accurately reflects the magnitude of the current flow.But as the current flows get larger, the small changes in the magnitudeof the current flow result in very small changes in electric potentialacross the flow, which become indistinguishable from current-inducednoise.

Hall Effect mechanisms enabling large current measurements make thesimultaneous measurements of small currents difficult. Thus, measuringlarge dynamic ranges, which would enable large amplitudes to be measuredwith very high resolution, is difficult using Hall Effect mechanisms.The need for efficient, accurate and sensitive current sensors is notmet by available sensors, including Hall Effect and discrete currentloop sensors. Such devices lack dynamic range. This means that if thedevices are configured to measure small currents, they cannot measurelarge ones. And if configured to measure large currents, they cannotresolve small ones.

The need for large dynamic range providing the simultaneous features ofmeasuring large amplitudes with high resolution is problematic. One ofthe significant factors at play compounding the problem of a highresolution and large signal range is circuit noise composed of thermalnoise and a combination of magnetic and electric field noise. As currentamplitudes get larger within a circuit, coupling from one circuit pathto another by radiated energy combined with I²R effects can render highresolution difficult to obtain.

Furthermore, the problems are exacerbated when attempting to measurehigh-current circuits using physically small sensors. Physically smallHall Effect sensors have limited maximum current capabilities and theyalso offer limited dynamic range. Physically small discrete currentloops are very difficult to productize because of a lack of definedphysical interface structures capable of carrying large currents.

Accurately measuring small differences in the magnitude of separatecurrent flows is a challenge that cannot be overcome by conventionalHall Effect devices because of their limited dynamic range and inabilityto handle large currents. Current loops are also challenged to providehigh resolution accurate measurement of large current flows because theradiated electromagnetic and electric field noise from nearby largecurrent flows is seen as circuit noise that masks the fine-resolutionsignals.

Additionally, in the typical application of existing technology, thehigh resolution of large current flows using discrete components or wireis difficult because physically locating the loop sensor so as to beperfectly orthogonal and concentric to the flux path is beyond currentmanual or automated technologies. The challenge is the asymmetry ofplacement of the wires in the current loop field.

A special challenge for current loops lies in the high resolution ofdifference currents between two AC conductors, one the supply and onethe return. Current Ground Fault Interrupter technologies implementsimultaneous counter-windings around a common movable core that trips acircuit switch to open upon a detectable current level. The physicalcomplexity and comparatively large size of simultaneous windings asalternative limits their use in low-cost, large-volume, high-currentcircuit applications demanding accurate high-resolution current-sensingcapabilities.

BRIEF SUMMARY

Embodiments of the present disclosure include a Low-Noise,Low-Frequency, Alternating Current Sensor which applies Faradayshielding and physical radiation-noise canceling as an implementation ofa planar current loop sensor disposed on a plurality of stackedsubstrates.

Characteristics that are present in embodiments include preciseorthogonal sensor placement relative to current-induced flux path,precise concentric placement of the flux concentrator relative to thetarget current conductor, the minimization of radiated flux from thecurrent transport conductors into and out of the target currentconductor relative to the flux concentrator using minimizing cornergeometries, the minimization of thermal dissipation by using optimizedskin effect transport conductor design and the reduction of thereception of radiated noise through the use of a nearlyfull-circumferential, multilayered circuit card-implemented Faradayshielding construction. Significant reduction of noise-radiated couplingwithin the circuit is achieved with separately grounded Faraday shieldradiation barriers to segregate high-current conductors from theassociated low signal-amplitude loop sensor conductors.

In an embodiment, a current sensor comprises a plurality of substrates,a first conductive path, a flux path comprising a first portionorthogonal to the first conductive path and a second portion, each ofthe first and second portions penetrating the plurality of substrates,an inductive sensor with a first loop oriented orthogonal to the secondportion of the magnetic flux path, an amplifier coupled to the inductivesensor, and a Faraday cage disposed between the first portion and thesecond portion of the flux path.

In another embodiment, a current sensor comprises a first substrate, afirst conductor, a magnetic flux conductor comprising a first portionorthogonal to the first conductor and a second portion, the secondportion penetrating the first substrate, an inductive sensor comprisinga first plurality of loops around the second portion of the magneticflux conductor on the first substrate, wherein the first plurality ofloops is orthogonal to the second portion of the magnetic fluxconductor, and a Faraday cage that encloses the first plurality of loopsand separates the first plurality of loops from the first conductor. Thefirst conductor may be positioned relative to the first portion of themagnetic flux conducting material such that when current flows throughthe first conductor, a first magnetic flux is induced in the magneticflux conductor. The magnetic flux conductor may further comprise a thirdportion that penetrates the first substrate and is orthogonal to asecond conductor. The second conductor may be positioned relative to thethird portion of the magnetic flux conductor such that when currentflows through the second conductor, a second magnetic flux is induced inthe magnetic flux conducting material, and a magnetic flux that isproportional to a difference between the first magnetic flux and thesecond magnetic flux is present in the second portion of the magneticflux conductor. The first plurality of loops may be arranged in a spiralshape around the second portion of the magnetic flux conductor.

The current sensor may further comprise a second conductor orthogonal tothe first portion of the magnetic flux conductor, and a distance betweenthe first conductor and the second portion of the magnetic fluxconductor is the same as a distance between the second conductor and thefirst portion of the magnetic flux conductor. The first and secondconductors may be supply and return lines for an alternating current,and an amount of magnetic flux flowing through the magnetic fluxconductor may be proportional to a difference between an amount ofcurrent flowing through the first conductor and an amount of currentflowing through the second conductor.

The current sensor may further comprise a second substrate, wherein theinductive sensor further comprises a second plurality of loops disposedon the second substrate, and the Faraday cage may extend between thefirst and second substrates.

In an embodiment, the current sensor further comprises an amplifierconfigured to amplify current in the inductive sensor. The amplifier maybe disposed on a third substrate outside the Faraday cage. The currentsensor may measure a magnitude of current flowing through the firstconductor.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying drawings are intended to convey the concept and are notintended as blueprints for construction as they are not drawn to scale:the drawings are typically exaggerated to show features that wouldotherwise be obscured. However, the foregoing aspects and many of theattendant advantages of the technologies described by this disclosurewill become more readily appreciated by reference to the followingdetailed descriptions, when taken in conjunction with the accompanyingdrawings, wherein:

FIG. 1 shows a plan view of an inductive loop-sensing currentmagnitude-detecting planar sensor including a complete Faraday cage thatisolates the flux-detecting loop from radiated energy emitted fromsources outside of the Faraday cage while the loop is shown coupled toan isolation, differential instrumentation amplifier as an integratedcircuit or a Chip-On-Board (COB) device.

FIG. 2 shows a side view of an inductive loop-sensing currentdifference-detecting planar sensor constructed using an implementationof a complete Faraday cage that isolates the flux-detecting loop fromradiated energy emitted from sources outside of the Faraday cage whilethe loop is shown coupled to an isolation, differential instrumentationamplifier as an integrated circuit or a Chip-On-Board (COB) device.

FIG. 3 illustrates a cut-away view of a core planar inductiveloop-sensing current difference-detecting circuit constructed using amultilayer circuit card providing isolating ground planes above andbelow the circuit conductors while providing a single sensor windingaround the flux-carrying ferrite core.

FIG. 4 illustrates a cut-away view of a core planar inductiveloop-sensing current difference-detecting sensor multi-loop circuitconstructed using a multilayer circuit card construction, usingisolating ground planes while providing a multi-loop sensor windingaround the flux-carrying ferrite core, which channels the flux of thetwo current-carrying conductors.

FIG. 5 shows a view of the inner construction of planar interconnectedground planes using drilled and plated-through vias to create a Faradayisolation cage.

FIG. 6 shows a plan view of an inductive loop-sensing currentdifference-detecting planar sensor constructed using an implementationof a complete Faraday cage that isolates the flux-detecting loop fromradiated energy emitted from sources outside of the Faraday cage whilethe loop is shown coupled to an isolation, differential instrumentationamplifier as an integrated circuit or a Chip-On-Board (COB) device.

FIG. 7 shows a plan view of an inductive multi-loop sensing currentdifference-detecting planar sensor constructed using an implementationof a complete Faraday cage, isolating the flux-detecting loop fromradiated energy emitted from sources outside of the Faraday cage whilethe loop is shown connected to an isolation, differentialinstrumentation amplifier as an integrated circuit or a Chip-On-Board(COB) device.

FIG. 8 shows a side view of the planar circuit presented in FIG. 7.

FIG. 9 shows a plan view of the sensing circuit of FIG. 6 where multipleloops are implemented on a single layer, which could be repeated on eachsensor layer of the circuit depicted in FIG. 7.

FIG. 10 shows a side view of a variation of the circuit depicted onFIGS. 6, 7 and 9, but using a 3-path, double-loop magnetic fieldcomponent rather than a 2-path single-loop magnetic field component.

FIG. 11 shows a plan view of the circuit presented in FIG. 10,illustrating that a 3-(or more) path magnetic circuit could be used witha multi-loop, multilayer sensor implementation.

FIG. 12A shows a single-loop flux-conducting path, and FIG. 12B shows adouble-loop flux-conductive path.

FIG. 13 shows a process of sensing or determining an amount of currentflowing through a conductor or sensing a difference in current flowingbetween two conductors.

DETAILED DESCRIPTION

The following list provides a number of specific descriptions andexamples of components that are present in the embodiments illustratedby the figures. The descriptions in the list are illustrative ofspecific embodiments, and should not be construed as limiting the scopeof this disclosure.

REFERENCE

Numerals Description  1 AC conductor representing one connectioncomponent (supply or return) of a circuit in which current is to bemeasured.  2 AC conductor representing one connection component (supplyor return) of a circuit in which current is to be measured.  3 Surfacesubstrate on which components could be mounted on the top or bottom sideand a ground plane 31 is plated on the opposite side.  4 Substratesupporting a high-current conductor 1 disposed on the top side.  5Substrate on which an inductive sensor 7, is plated on the top side andshielded on the bottom side by a ground plane 31.  6 Substratesupporting a high-current conductor 2 plated in heavy copper anddisposed on the bottom side, with a Faraday cage pass-throughterminating on the ground plane 31 on the top side.  7 Inductive sensorconductor orthogonal to the flux-conducting orthogonal path 8.  8Flux-conducting orthogonal path.  9 Exposed circuit card substrate.  10A terminating “turn” section of a multi-turn inductive sensor orthogonalto flux- conducting orthogonal path 8.  11 A non-terminating “turn”section of a multi-turn inductive sensor orthogonal to flux-conductingorthogonal path 8.  12 A complementary terminating “turn” section of amulti-turn inductive sensor orthogonal to flux-conducting orthogonalpath 8.  13 A vertical drilled and plated-through via connecting returncircuit 22 with a terminating horizontal “turn” of an inductive sensor. 14 A vertical drilled and plated-through via connecting successivehorizontal “turns” or turn components 10, 11, 12 of an inductive sensor. 15 A Faraday cage  16 Insulation layer  17 A via created to formvertical “cage” components of a Faraday cage 15 isolating an inductivesensor.  18 An isolation gap between a Faraday cage and an intermediatecircuit board layer on which other circuit components may be located. 20 A Chip-On-Board (COB) or Integrated Circuit (IC) differentialinstrumentation amplifier.  21 A first conductive element or terminalarm connecting a current loop sensor to a differential instrumentationamplifier 20.  22 A second conductive element or terminal arm that is areturn or companion circuit element to the first conductive element 21. 23 COB or IC differential, instrumentation amplifier terminatingcontact.  31 Ground plane on one layer of circuit board.  32 Verticalvia (13, 14) transition to connective circuit components 21 and 22. 100Current sensor

Embodiments of the present disclosure are directed towards a largedynamic-range inductive current sensor 100. The technology includes theprocedure for creating an inductive sensor of nominal sensitivity, whichincludes an orthogonal inductive sensor 7, precisely placed around ahigh-permeability flux-conducting path component 8 that is orthogonal toa current-carrying conductor 1 (see FIG. 3) and embodiments in whichturns of an inductive sensor 7 are disposed on several differentsubstrates (see FIG. 4) for greater sensitivity.

The present disclosure describes embodiments that have at least twoapplications. The first application, an embodiment of which is shown inFIG. 1, is the measurement of the magnitude of currents with very highresolution, and can be applied to relatively high current flows as acurrent sensor 100 with larger dynamic range than conventional sensors.The second application is precise measurement of a difference in currentbetween a supply and a return conductor. Embodiments of a differencesensing current sensor are shown in FIGS. 6, 7, 9 and 11.

Embodiments of the present disclosure use the precision capabilities ofmultilayer photo-resist printed circuit board construction, along withthe macro design considerations of Faraday electromagnetic and electricfield isolation theory. These technologies can be combined to create a3-dimensional physical construction (FIGS. 2 and 8) that implements aFaraday cage 15 (FIG. 5), blocking outside radiation, as well asimplementing an architecture of planar component structures to affectthe reduction of magnetic, electric field and thermally inducedself-noise inside the cage. The constructed Faraday cage 15 provideselectromagnetic and electric field isolation around one or more of theloops of an inductive loop sensor 7 using ground planes terminating orsupporting a “cage” of drilled, plated-through and filled viaspositioned appropriately around the sensor, forming an extensiveelectromagnetic, electric field and thermal energy dissipativestructure. Further, the capabilities of current photo-resist circuitcard technologies provide a significant improvement over both automatedand manual component placement technologies to optimize intentional fluxcoupling.

FIG. 1 and FIG. 6 reveal plan views of the via-constructed Faraday cage15 and planar current loop sensor 7. The vias 17 are shown but theground planes as well as the circuit surfaces of inner layers 4, 5 and 6of FIG. 3 are rendered transparent. Although the insulation layer 16between the planes is only shown in FIG. 4, the insulation layer 16 maybe present between every set of adjacent substrates. In an embodiment,the insulation layer 16 comprises an epoxy material, but other materialsare possible. For example, the insulation layer 16 may comprise apolymer material that adheres to the substrates, and the layer mayprovide structural integrity as well as electrical isolation betweencomponents.

Although not shown in the figures, the circuit card substrate 9 mayinclude copper traces and various circuit components, and adielectric-matched epoxy binder 16 may be disposed between adjacentsubstrates to provide electrical isolation between conductors 1 and 2,flux-conducting orthogonal path 8 and ground planes 31. In anembodiment, the circuit card substrate 9 is a polyimide substrate. Thematerial of the insulation layer 16 may have a dielectric constant thatmatches the dielectric constant of the parent circuit substrate 9.

As can be seen in FIG. 1, the high resolution construction and placementof the inductive sensor 7 and conductor 1 and flux-conducting orthogonalpath 8 enable a precision placement into a concentric fluxemission-capture relationship, enabling the amplitude measurement oflarge currents. In FIG. 1, conductor 1 is disposed towards an outer edgeof the substrate 9 and is orthogonal to a portion of the flux-conductingorthogonal path 8 that extends through the circuit layers.

Some embodiments of the present disclosure are directed to a differencecurrent sensor. For example, the embodiments shown in FIG. 6 and FIG. 4,conductors 1 and 2 are both oriented orthogonal to the flux-conductingorthogonal path 8 and at a different elevation than the connectivecomponents of inductive sensor 7 or the extension circuit connections 21and 22. One or both of conductors 1 and 2 may be above or below segmentsof the Faraday cage 15. For example, FIG. 2 shows an embodiment in whichsecond conductor 2 is disposed below the Faraday cage 15. In FIG. 6 thecurrent loop sensor 7 is shown on an internal layer with vertical riservias 32 connecting the embedded loop sensor 7 to the circuit layerconnective circuit components 21 and 22, which extend the connection ofthe loop sensor 7 to the COB or IC differential instrumentationamplifier 20.

When the current sensor 100 is a difference current sensor, firstconductor 1 may be coupled to a supply line and second conductor 2 maybe coupled to a return line so that supply and return currents of anexternal device run through the conductors. The current running throughfirst conductor 1 causes a first electromotive force that induces amagnetic flux in flux-conducting orthogonal path 8 in a first direction,and second conductor 2 causes a second electromotive force that inducesa magnetic flux in flux-conducting orthogonal path 8 in a seconddirection opposite to the first direction. Equal components of opposingelectromotive forces effectively cancel one another out, so that whencurrent is evenly balanced between the first and second conductors 1 and2, no magnetic flux flows through flux-conducting orthogonal path 8.

On the other hand, when an electrical fault such as a short or groundfault occurs in the electrical path of the first and second conductors 1and 2, the supply and return currents are no longer balanced. In thiscase, the electromotive forces acting on the flux-conducting orthogonalpath 8 do not cancel each other out, and the greater force of the twoconductors will cause a difference flux to flow through flux-conductingorthogonal path 8. This difference flux is sensed by inductive sensor 7.Due to the sensitivity of the current sensor 100, relatively smalldifferences in current can be sensed quickly and accurately. Forexample, when current on the order of 5-50 amps flows through the firstand second conductors, embodiments described by the present disclosurecan sense a difference as low as 2-3 mA, or 4 orders of magnitude lowerthan the current flowing through the conductors. Embodiments of thepresent disclosure can be scaled to sense currents outside thisrange—for example, MEMS scale devices could accurately sense currents inthe milliamp range, and larger scale devices could accurately sensecurrents above 50 amps. In such embodiments, the current sensor 100 maysense differences or fluctuations of 3 or 4 orders of magnitude lowerthan the current flowing through the conductors.

When the current sensor 100 is used to sense a difference in supply andreturn current paths, the conductors may be positioned symmetrical tothe flux-conducting orthogonal path 8. For example, FIGS. 2, 3, 4 and 8show embodiments in which the conductors are symmetrical with respect toa horizontal plane that runs through the center of and is orthogonal tothe flux-conducting orthogonal path 8. In such an embodiment, theconductors are symmetrical with respect to a length direction of aportion of the flux path.

FIG. 10 shows an embodiment in which flux-conducting orthogonal path 8comprises two flux-conducting loops that share a central flow path. Insuch an embodiment, the first and second conductors may be positionedsymmetrically with respect to a horizontal direction of theflux-conducting loops 8 as seen in FIG. 10.

In an embodiment, the amplifier 20 may be coupled to circuitinterruption circuitry, and the current sensor or associatedinterruption circuitry 100 may be configured to interrupt a circuit whena particular amount of difference current is detected. Accordingly,embodiments of the current sensor 100 may protect sensitive equipment orpersonnel from being damaged by ground faults or shorts in a circuitthat carries current.

Furthermore, the current sensor technologies described by the presentdisclosure are scalable, and can be applied to a range of currents. Forexample, while the embodiments shown in the figures are described withrespect to PCB technologies and manufacturing techniques, deposition,doping, polishing and etching techniques can be applied to fabricate anembodiment that is a micro-electromechanical system (MEMS) device.

Although the figures show conductors 1 and 2 as having round shapes forthe convenience of illustration, embodiments of the conductors may havea generally flat shape in which the width of the conductors issubstantially greater than the thickness of the conductors. In such anembodiment, a round conductive wire of a device through which currentflow is being measured may be electrically coupled to a terminal (notshown) that is provided on the circuit board on which the conductor 1 or2 is disposed, or on a package or assembly associated with the circuitboard. In an embodiment, conventional outlet plugs can be used to couplea current sensor 100 to the electrical path of an external device. Inanother embodiment, the current sensor 100 is integrated into theelectrical circuitry of a device through which current flow is to bemeasured.

Plan views in FIGS. 6, 7 and 9 show the conductors 1 and 2 as beingoffset from one another with respect to the circuit board plane for theconvenience of illustration, so that both conductors are visible in theplan views. In an embodiment, the distance between the first conductor 1and flux-conducting orthogonal path 8 is the same as the distancebetween the second conductor 2 and flux-conducting orthogonal path 8.

In some embodiments, the conductors may have a width-to-thickness ratio,or aspect ratio, of 10:1, 50:1, 100:1 or more. The precision ofphoto-resist printing allows the creation of conductors having awidth-to-thickness ratio of greater than 100. Such conductor geometriesmay minimize the emission of non-uniform flux fields due to conductorcorner effects. Embodiments are not limited to a specific conductorshape, but current sensing may be more accurate when the conductors lacksharp corners and have high width-to-thickness ratios. The material forconductors 1 and 2 may be a conductive material such as copper orsilver.

In an embodiment, conductors 1 and 2 may comprise a superconductingmaterial. The superconducting material may be maintained in asuperconducting state by lowering the temperature of the conductors,which has an additional benefit of reducing thermal noise. At highertemperatures, superconductivity can be imparted by applying a pressureto the conductors. For example, recent advances in superconductingtechnology have established that superconductivity can be obtained atroom temperature by applying sufficient pressure to hydrogen-richmaterials. Using superconductors as the conductors 1 and 2 can improvecurrent sensing accuracy and sensitivity.

Conductors 1 and 2 may be implemented as planar conductors having across-sectional area such that the specific resistance is relativelylow. In an embodiment, the resistance is low enough that at themaximum-rated current flow the thermal energy dissipated by theconductor material into the circuit card does not exceed the combinedconductive and convective cooling capacity of the circuit card, whichwould cause the temperature of the circuit card to rise.

In an embodiment, the conductors 1 and 2 are implemented as wide, thincopper conductors to minimize the magnetic effects of the current flowat the corners of the conductors, while the flux-conducting orthogonalpath 8 has a cross-sectional area at least equal to 2 times thecross-sectional area of the high-current ribbon conductor. In otherembodiments, the flux-conducting orthogonal path 8 has a cross-sectionalarea that is 5, 10 or more times the cross-sectional area of theconductors. An embodiment in which a conductor has a highwidth-to-thickness ratio and the flux-conducting orthogonal path 8 has across-sectional area that is at least twice the cross-sectional area ofthe conductors may minimize radiated electromagnetic noise andself-induced thermal noise.

FIGS. 12A shows an embodiment of a flux-conducting orthogonal path 8that comprises a single loop, as seen in FIGS. 1-4 and 6-9. Theembodiment shown in FIG. 12A has an oval shape comprising two connectingparts 80 that are coupled to one another through penetrating parts 82,which penetrate one or more substrate layer. The radius or precise shapeof the connecting parts 80 is not particularly limited so long as theyprovide an effective pathway for magnetic flux between the penetratingparts 82.

Each of the connecting parts 80 may be formed separately from thepenetrating parts 82 and bonded to the connecting parts in assembly. Thepenetrating parts 82 and the connecting parts 80 may be fabricated asdiscrete parts and assembled into the current sensor 100 by insertingthe penetrating parts into holes disposed in one or more substrate ofthe current sensor, and subsequently attaching the connecting parts tothe penetrating parts by, for example, a friction fit, weld, or adhesivebond. When an adhesive is used, the sizes of the components may beenlarged compared to a friction fit assembly to compensate for theresistance introduced by the adhesive interface. In another embodiment,the penetrating parts 82 may be formed by depositing a magnetic fluxconducting material into holes that are laser-drilled through aplurality of stacked substrates, and the turns 80 may be formed byplacing or depositing a conductive material over exposed ends of thepenetrating parts 82.

FIG. 12B shows an embodiment of a flux-conducting orthogonal path 8 thatcomprises two loops, as seen in FIGS. 10-11. In such an embodiment, thetwo loops share a central penetrating part 84 that is coupled to aninductive current sensor 7. When current flows through conductors inopposite directions and the conductors are coupled to separatepenetrating parts 82, flux induced by the conductors meets in thecentral penetrating part 84. When the current in the conductors isequal, the opposing flux paths cancel one another out, but when thecurrent in the conductors is different, an amount of flux will flowthrough the central penetrating part 84 that is proportional to thedifference.

Also shown in FIG. 1 is a loop of inductive sensor 7. The loop is asemi-circular conductive structure that extends around a portion offlux-conducting orthogonal path 8. The loop is coupled to two terminals23 of amplifier 20 through conductive elements 22 and 21, which extendfrom ends of the sensor 7. In an embodiment, the conductive elements 22and 21 are conductive traces on a circuit board. The sensor 7 may be aplanar conductive structure that is orthogonal to flux-conductingorthogonal path 8 so that magnetic flux through the flux-conductingorthogonal path 8 induces a current to flow through inductive sensor 7.

The amount of current flowing through sensor 7 may be substantiallylower than the amount of current flowing through a conductor 1, or thedifference in current between first conductor 1 and second conductor 2.Therefore, amplifier 20 is used to amplify the current from sensor 7 sothat the current can be sensed accurately.

The planar sensor loop 7 may have a width-to-thickness ratio that is nogreater than 10:1. In some embodiments, the planar sensor loop 7 mayhave a width-to-thickness ratio of 5:1, 2:1, 1:1, 1:2, 1:5, 1:10, orgreater than 1:10. In some embodiments, the planar sensor loop 7comprises one or more layer of copper material that is printed onto acircuit board. In another embodiment, the sensor loop 7 may comprise adiscrete component that is placed on a circuit board, which canfacilitate relatively high width-to-thickness ratios.

The way that planar sensor 7 is arranged within the current sensor 100enhances the accurate detection of magnetic energy: the conductor of thesensor 7 will have a small flux-induced current which will createminimal magnetic or thermal self noise. Therefore, even though thesensor 7 is disposed within the Faraday cage 15, the amount of noisegenerated by sensor 7 has a minimal effect on the signal that istransmitted to the amplifier 20.

To enhance the accurate coupling of the current-induced magnetic flux,loops of the inductive sensor 7 may be as close to being perfectlyorthogonal and concentric with the flux-conducting orthogonal path 8 aspossible. The precision of current photo-resist printing technologiesenables the construction of a planar inductive current sensor as asignificant improvement in relative positioning over all automated ormanual discrete component placement technologies currently available.

For increased sensitivity, embodiments may include a multilayerinductive sensor pickup coil or loop. For example, FIG. 4 illustrates anembodiment in which multiple planar turns of the sensor coil or loopdisposed on different levels are implemented such that each turn isexactly orthogonal to the flux-conducting orthogonal path 8. Similarly,FIG. 9 shows an embodiment in which multiple loops are disposed on asingle substrate. A multi-turn, multilayer inductive sensor coil cansignificantly improve flux coupling and minimize the cross coupling offlux energy when all of the sensor coils or loops are similarlyorthogonal to the flux-conducting orthogonal path 8.

Precisely aligning multiple loops on multiple layers is difficult toimplement using discrete physical components or wire. Therefore,embodiments of the present application may use photolithographictechniques to form the conductive loops, or use photolithographictechniques to provide a precisely located trench in which discrete loopelements are placed.

Multiple embodiments of the inductive sensor 7 are possible. Forexample, FIG. 3 illustrates an embodiment in which the inductive sensorcomprises a single turn section and is disposed on only one substrate ofa current sensor. FIG. 4 illustrates an embodiment in which inductivesensor 7 comprises a plurality of turn sections 10, 11 and 12 disposedon different substrates.

Although three turns are shown in FIG. 4, embodiments may comprise twoturns, five turns, or even a hundred or more turns. Each turn of theinductive sensor 7 increases the amount of current that is induced inthe inductive sensor by magnetic flux flowing through theflux-conducting orthogonal path 8, so providing additional turns canincrease the sensitivity of the current sensor 100. Furthermore,practical considerations in plating techniques may limit the thicknessto which a given turn can be formed, and such limitations can beaddressed by providing multiple turns on different substrate layers.

When multiple turns are disposed on different substrate layers, thoseturns may be electrically coupled to one another through verticalconductive paths 14. The vertical conductive paths 14 may be coupled byplated-through vias in the substrates.

Also shown in FIG. 4 is a configuration in which the turns 10, 11 and 12and the vertical conductive paths 14 are oriented so that current flowsin a continuous path through the turns. For example, with respect to theorientation shown in FIG. 4, a first conductive path extends from theright or first end of the uppermost turn 10 that is coupled to a firstterminal of an amplifier 20, and a vertical conductive path 14 extendsdownwards from the left or second end of the uppermost turn 10 and iscoupled to the left or second end of the middle turn 11. Anothervertical conductive path 14 extends from the right side or first end ofthe middle turn 11 and is coupled to the first end of the bottom turn12. A second conductive path extends from the second end of bottom turn12 and is coupled to a second terminal of the amplifier 20. Accordingly,inductive sensor 7 comprises a plurality of turns disposed on differentsubstrates that are coupled to one another to provide a path throughwhich current flows and is sensed by amplifier 20.

In the embodiment shown in FIG. 11, multiple turns are disposed on thesame substrate layer. The inductive sensor 7 depicted in FIG. 11 has aspiral shape that is concentric with the flux-conducting orthogonal path8. In addition, first and second ends of the spiral shape may be coupledto vertical conductive paths that are disposed on different planes—forexample, one path may be disposed on the plane of an upper surface of asubstrate, while the other path may be disposed on a plane of a lowersurface of the same substrate, or on an upper or lower surface of adifferent substrate.

The Faraday cage 15 may be constructed using multilayer printedphoto-resist circuit board printing technologies. The ground plane 31 onthe bottom of layer 3 forms the top of the Faraday cage 15 and isphysically connected through the arrangement of plated-through vias asthe Faraday cage walls to the ground plane 31 on the top of circuitboard layer 6 which forms the bottom of the Faraday cage. The resultingconstruction is a Faraday cage 15 that extends through a plurality ofsubstrate layers and provides full electric and magnetic noise isolationfor sensing components and conductive elements disposed within the cage.The Faraday cage 15 passes through circuit board layer 5 withoutcreating an electrical connection. The Faraday cage may be isolated byan isolation gap 18 from the copper plating on either side of circuitboard layer 5. Thus layer 5 is available to support circuit or inductivesensor components or both.

In an embodiment, the effect of the Faraday cage 15 is created by asystem of plated-through vias or holes arranged in a pattern thatprovides a nearly full-ring magnetic flux and electric field shield forcircuit paths of interest. The nearly full-ring shield effectivelyprovides the equivalent of a screen wall to radiated energy. Theconstructed screen wall may comprise a series of holes spaced about twohole diameters apart along the circumference of two concentric circleswhose radii differ by about one and one-half diameters of the filled viaholes positioned orthogonally to both the circumference and the radiuslines, such that the holes along the inner circle are set in between theholes in the outer circle. The spacing between adjacent vertical riservias 17 may be, for example, greater than one via diameter and less thanthree via diameters, or greater than 1.5 diameters and no more than 2.5diameters.

In some embodiments, each of the vertical riser vias 17 in the outerlayer are disposed at radial locations corresponding to midpointsbetween adjacent vertical riser vias in the inner layer. Furthermore,adjacent vertical riser vias This physical arrangement of theplated-through via holes provides a block to radiated electromagneticenergy without substantially weakening the circuit board materialbetween the two circles.

In an embodiment, the Faraday cage 15 encloses every turn of theinductive sensor 7, as well as the vertical riser vias 32 that coupleturns of the inductive sensor that are disposed on different substrates,and portions of the penetrating parts 82 that run through turns of theinductive sensor. In the embodiment shown in FIG. 1, enclosing both theinductive sensor 7 and the vertical riser vias 32 results in anasymmetrical Faraday cage with a first portion that encloses theinductive sensor 7 and a second portion that extends from the firstportion and encloses the vertical riser vias 32.

FIG. 13 illustrates an embodiment of a process 1300 for sensing ordetermining an amount of current flowing through a conductor, or sensinga difference in current flowing between two conductors. Process 1300 mayinclude providing an alternating current through one or both ofconductors 1 and 2, which may be supply and return currents for acircuit, at S1302. The current from the first conductor 1 induces afirst flux in flux-conducting orthogonal path 8 which is orthogonal tothe first conductor at S1304, and when a second conductor 2 is present,the second conductor induces a second flux in the flux-conductingorthogonal path 8 at S1306.

The first and second fluxes combine in the flux-conducting orthogonalpath 8 at S1308, and may either cancel each other out when they areequal. When the fluxes are not equal, a difference flux flows throughflux-conducting orthogonal path 8 which induces a current to flow ininductive sensor 7 at S1310. The inductive sensor 7 may be couple to anamplifier that amplifies the current at S1312 to determine a differencein current between the first and second conductors 1 and 2. When currentonly flows through a single conductor, the process 1300 may determine amagnitude of the current flowing through the conductor.

In some embodiments, determining the amount of current flowing throughthe single conductor, or determining the difference in current betweentwo conductors may further comprise translating the amplified signalfrom inductive sensor 7 into a current value that corresponds to anactual current level in the first conductor, or an actual difference incurrents, at S1314. The translation may be performed by a circuit or aprogrammable controller.

Process 1300 may further comprise shielding components involved insensing the currents at S1316. In particular, S1316 may includeshielding turns of an inductive sensor 7 by a Faraday cage that enclosesthe inductive sensor and any vertical conductive paths 14 that extendbetween turns of the inductive sensor that are disposed on differentsubstrates. The Faraday cage may comprise vertical elements that arevias extending through at least one substrate layer, and ground planesthat are co-planar with the substrates as top and bottom surfaces of theFaraday cage.

1. A current sensor comprising: a first substrate; a first conductor; amagnetic flux conductor comprising a first portion orthogonal to thefirst conductor and a second portion, the second portion penetrating thefirst substrate; an inductive sensor comprising a first plurality ofloops around the second portion of the magnetic flux conductor on thefirst substrate, wherein the first plurality of loops is orthogonal tothe second portion of the magnetic flux conductor; and a Faraday cagethat encloses the first plurality of loops and separates the firstplurality of loops from the first conductor.
 2. The current sensor ofclaim 1, wherein the first conductor is positioned relative to the firstportion of the magnetic flux conducting material such that when currentflows through the first conductor, a first magnetic flux is induced inthe magnetic flux conductor.
 3. The current sensor of claim 2, whereinthe magnetic flux conductor further comprises a third portion thatpenetrates the first substrate and is orthogonal to a second conductor.4. The current sensor of claim 3, wherein the second conductor ispositioned relative to the third portion of the magnetic flux conductorsuch that when current flows through the second conductor, a secondmagnetic flux is induced in the magnetic flux conducting material, and amagnetic flux that is proportional to a difference between the firstmagnetic flux and the second magnetic flux is present in the secondportion of the magnetic flux conductor.
 5. The current sensor of claim1, further comprising a second conductor orthogonal to the first portionof the magnetic flux conductor, and a distance between the firstconductor and the second portion of the magnetic flux conductor is thesame as a distance between the second conductor and the first portion ofthe magnetic flux conductor.
 6. The current sensor of claim 5, whereinthe first and second conductors are supply and return lines for analternating current.
 7. The current sensor of claim 6, wherein an amountof magnetic flux flowing through the magnetic flux conductor isproportional to a difference between an amount of current flowingthrough the first conductor and an amount of current flowing through thesecond conductor.
 8. The current sensor of claim 1, further comprising:a second substrate, wherein the inductive sensor further comprises asecond plurality of loops disposed on the second substrate.
 9. Thecurrent sensor of claim 8, wherein the Faraday cage extends between thefirst and second substrates.
 10. The current sensor of claim 1, furthercomprising: an amplifier configured to amplify current in the inductivesensor.
 11. The current sensor of claim 10, wherein the amplifier isdisposed on a third substrate outside the Faraday cage.
 12. The currentsensor of claim 1, wherein the current sensor measures a magnitude ofcurrent flowing through the first conductor.
 13. The current sensor ofclaim 1, wherein the first plurality of loops is arranged in a spiralshape around the second portion of the magnetic flux conductor.
 14. Thecurrent sensor of claim 1, further comprising: a second conductor,wherein the first and second conductors are supply and return lines foran alternating current, and wherein the first and second conductors havea width-to-thickness ratio of at least 50:1.
 15. A current sensor,comprising: a first substrate; a second substrate; a first conductor; asecond conductor; a magnetic flux conductor comprising a first portionorthogonal to the first conductor and a second portion orthogonal to thesecond conductor, the second portion penetrating the first and secondsubstrates; an inductive sensor comprising a first plurality of loopsaround the second portion of the magnetic flux conductor on the firstsubstrate, and a second plurality of loops around the second portion ofthe magnetic flux conductor on the second substrate, wherein the firstand second plurality of loops are orthogonal to the second portion ofthe magnetic flux conductor; and a Faraday cage that isolates the firstplurality of loops and the second plurality of loops from the first andsecond conductors.
 16. The current sensor of claim 15, wherein adistance between the first conductor and the second portion of themagnetic flux conductor is the same as a distance between the secondconductor and the first portion of the magnetic flux conductor.
 17. Thecurrent sensor of claim 15, wherein the magnetic flux conductor furthercomprises a third portion that is orthogonal and adjacent to the secondconductor.
 18. The current sensor of claim 17, wherein a distancebetween the first conductor and the first portion of the magnetic fluxconductor is the same as a distance between the second conductor and thethird portion of the magnetic flux conductor.
 19. The current sensor ofclaim 15, further comprising an amplifier disposed on a third substratethat is stacked with the first and second substrates.
 20. The currentsensor of claim 15, wherein the first and second conductors have awidth-to-thickness ratio of at least 50:1.